Sorghum is a promising alternative to maize for bioenergy production in Europe; however, its use is currently limited by poor adaptation to low temperatures during and after germination. We collected multi-trait phenotype data under optimal and suboptimal temperatures in a genetically diverse recombinant inbred line (RIL) mapping population showing contrasting segregation patterns for pre-and post-emergence chilling tolerance. Germination, emergence, seedling development, root architecture and seedling survival were assessed in two different seedlots. Emergence and root establishment were found to be the key determinants of development and survival under chilling stress. Highly interactive epistatic quantitative trait loci (QTL) hotspots, including a previously unknown QTL on Sb06 with a significant effect on prolonged chilling survival, were found to regulate different physiological mechanisms contributing to maintenance of growth and development despite the chilling temperatures. The major QTL regions harbour promising candidate genes with known roles in abiotic stress tolerance. Identification of loci in the QTL hotspot regions conferring maintenance of cell division and growth under early chilling stress represents a promising step towards breeding for successful establishment of sorghum in temperate climates.
Sorghum (Sorghum bicolor L. Moench) is regarded a drought-tolerant alternative to maize as a bioenergy and fodder crop, but its early-stage chilling sensitivity is obstructing a successful implementation in temperate areas. While several studies have identified quantitative trait loci (QTL) underlying chilling tolerance-related traits in sorghum lines, little is known about the inheritance of these traits in F 1 hybrids. We have conducted a comprehensive approach to analyse heterosis, combining ability and the relation between line per se and hybrid performance for emergence and early shoot and root development comprising both field trials and controlled environment experiments including chilling tests. To our best knowledge, this is the first study analysing heterosis for sorghum root parameters under chilling. Our results show that most traits are heterotic and that the midparent values are rather poor predictors of hybrid performance. Hybrid breeding programmes should focus on efficient GCA tests and the establishment of genetically diverse pools to maximise heterosis rather than on a too strict selection among lines based on their per se performance. The medium-to-high heritabilities estimated for seedling emergence and juvenile biomass suggest that a robust breeding progress for these complex traits is feasible.
The sensitivity of sorghum to pre-flowering cold stress, resulting in reduced pollen viability and poor seed set, is a major constraint for expanding growing areas into higher altitudes and latitudes. Nevertheless, compared to juvenile cold tolerance, reproductive cold tolerance in sorghum has received much less attention so far, and very little is known about its inheritance in F1-hybrids. We have composed a representative factorial (n = 49 experimental F1-hybrids) for a comprehensive study on heterosis and combining ability for crucial tolerance traits as spikelet fertility (panicle harvest index), seed yield and pollen viability, using field trials in stress- and control environments in Germany and Mexico as well as climate chamber experiments. Our results indicate a heterotic and rather dominant inheritance of reproductive cold tolerance in sorghum, with strong effects of female general combining ability (GCA) on F1-hybrid performance in our material. These findings, together with the comparatively low contribution of specific combining ability (SCA) effects and high heritability estimates, suggest that robust and efficient enhancement of reproductive cold tolerance is feasible via hybrid breeding.
Sorghum (Sorghum bicolor L. Moench) is a promising novel crop for Central Europe. However, enhancements in cold tolerance and early maturity are essential for a successful adaptation to cooler climates. We scored a broad sorghum diversity set (n = 338) for early chilling tolerance, high-latitude adaptation, and bioenergy related agronomical traits in multi-environment trials. Our results show a high phenotypic variation and medium to high heritabilities for most traits, indicating that a robust breeding progress is feasible. Several public accessions with a good adaptation to cooler climates were identified, which can serve as valuable base material for sorghum breeding in temperate areas. Genome-wide association studies reveal a polygenic (quantitative) character for most of the traits, confirming previous studies. Hence, for practical breeding, it will be difficult to conduct efficient marker-assisted selection for temperate-adaptation traits in genetically diverse material.
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